Such machines once took up large spaces inThe pressing concerns about the presence of unhealthy microbial pathogens in air and water are increasingly being addressed by the application of ultraviolet (UV) light treatment systems in municipal water treatment plants, office buildings and homes.

There is a growing concern about water due to the rapid decline of readily available potable water throughout the world. The use of UV disinfection technology promises to help make drinking water a more sustainable resource in regions where modern water treatment systems are in place. UV systems are also used for the removal of chemicals such as chlorine and ozone, and can be used to remove taste and odor compounds.

A relatively recent material shift to fused quartz has enabled UV light generation to become more effective in water or air treatment. A clear vitreous solid, formed by melting pure quartz, fused quartz can withstand high temperatures and is highly transparent to ultraviolet radiation. Fused quartz, a form of silica, is actually a non-crystallized form of SiO₂. The material, which in high grade (low impurities) is used in fiber-optic cables, can withstand much greater temperatures than typical glass, making it perfect for containing high-heat light sources. It is the preferred material where light transmission is concerned, because the transparency of quartz provides full spectral transmission.

Silica pure

Fused quartz materials are available in diameters, wall thicknesses and lengths to fit custom applications.

In some cases, the use of quartz glass translates to more than twice the amount of UV output when compared to standard germicidal lamps of the same length.

"In most designs, the ultraviolet light generator is a tubular lamp," said James Horvath, president of Technical Glass Products, Painesville, Ohio. "The lamp tubes are fitted or enveloped with quartz sleeves, a very simple operation with tube length, ID and wall thickness specified by the engineer in accordance with the system light fixtures. Typical sizes range from 18 to 45 mm ID with wall thicknesses between 1.25 and 1.50 mm, and are available in-stock with larger suppliers of fused quartz."

In terms of water-borne pathogens, UV radiation, in cost-effective doses, effectively inactivates common pathogens such as Cryptosporidium, parasites that cause the intestinal infection cryptosporidiosis; Giardia, protracted, intermittent diarrhea suggestive of malabsorption, which can cause dysentery; and most bacterial pathogens.

Among common airborne pathogens, it is held that UV lights reduce concentrations of airborne contaminants by as much as 5 percent (remaining from prior stages of treatment).

Although quartz may be considered a commodity material, there can be a quality difference. "Using the best raw materials, fused quartz is one of the purest materials available, having a nominal purity of up to 99.996 percent," said Horvath. "The purity of fused quartz is highly beneficial to optical applications including light transmission, which makes it ideal for applications such as fiber optics, photovoltaic (e.g., solar and UV), as well as stringent laboratory uses."

Horvath believes the purity of quartz is superior to that of borosilicate products. He added that the optical purity of quartz may be equally important to many users in laboratory environments because a relatively broad range of light wavelengths pass unimpeded through clear material, which is especially important in UV disinfection applications. PE